Engines may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system, a process referred to as exhaust gas recirculation (EGR), to reduce regulated NOx emissions. The particulate matter generated in a cylinder with EGR is highly dependent on the amount of EGR and increases exponentially if the EGR is not controlled. To adhere to increasingly stringent regulations, while optimizing fuel consumption, component reliability and control strategy complexity, it is desirable to minimize the cylinder-to-cylinder emissions variation in a multi-cylinder engine. This can be achieved by delivering a uniform and controlled amount of EGR to all the cylinders.
In some engine systems, a group of one or more cylinders may have an exhaust manifold that is exclusively coupled to an intake passage of the engine such that the group of cylinders is dedicated, at least under some conditions, to generating exhaust gas for EGR. Such cylinders may be referred to as “donor cylinders.” Other cylinders may have an exhaust manifold that is exclusively coupled to an exhaust passage of the engine, referred to as “non-donor cylinders.” Typically, an equal number of donor and non-donor cylinders may be present in the engine; for example, in a V-12 engine, one cylinder bank (six cylinders) may be comprised of donor cylinders while the other cylinder bank (also six cylinders) may be comprised of non-donor cylinders. This type of arrangement may lead to variation in the cylinder-to-cylinder amount of delivered external EGR as well as cylinder-to-cylinder variation in the amount of trapped in-cylinder EGR.